INVESTMENTS - Fair Value and Gross Unrealized Losses for Securities That Have Been in Continuous Unrealized Loss Position (Detail) - Fixed maturity securities - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Jun. 30, 2020
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		$ 12,646
Total Unrealized Losses		871
Less than 12 months Fair Value		9,096
Less than 12 months Unrealized Losses		492
12 months or longer Fair Value		3,550
12 months or longer Unrealized Losses		379
Total Fair Value	$ 7,190
Total Unrealized Losses	385
Less than 12 months Fair Value	3,423
Less than 12 months Unrealized Losses	178
12 months or longer Fair Value	3,767
12 months or longer Unrealized Losses	207
Yen-denominated | Municipalities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		144
Total Unrealized Losses		8
Less than 12 months Fair Value		131
Less than 12 months Unrealized Losses		7
12 months or longer Fair Value		13
12 months or longer Unrealized Losses		1
Total Fair Value	80
Total Unrealized Losses	3
Less than 12 months Fair Value	80
Less than 12 months Unrealized Losses	3
12 months or longer Fair Value	0
12 months or longer Unrealized Losses	0
Yen-denominated | Public utilities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		799
Total Unrealized Losses		15
Less than 12 months Fair Value		799
Less than 12 months Unrealized Losses		15
12 months or longer Fair Value		0
12 months or longer Unrealized Losses		0
Yen-denominated | Sovereign and supranational
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		219
Total Unrealized Losses		5
Less than 12 months Fair Value		219
Less than 12 months Unrealized Losses		5
12 months or longer Fair Value		0
12 months or longer Unrealized Losses		0
Yen-denominated | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		3,584
Total Unrealized Losses		319
Less than 12 months Fair Value		2,753
Less than 12 months Unrealized Losses		205
12 months or longer Fair Value		831
12 months or longer Unrealized Losses		114
Total Fair Value	1,828
Total Unrealized Losses	89
Less than 12 months Fair Value	1,828
Less than 12 months Unrealized Losses	89
12 months or longer Fair Value	0
12 months or longer Unrealized Losses	0
Yen-denominated | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		1,647
Total Unrealized Losses		153
Less than 12 months Fair Value		1,394
Less than 12 months Unrealized Losses		128
12 months or longer Fair Value		253
12 months or longer Unrealized Losses		25
Total Fair Value	636
Total Unrealized Losses	31
Less than 12 months Fair Value	636
Less than 12 months Unrealized Losses	31
12 months or longer Fair Value	0
12 months or longer Unrealized Losses	0
Yen-denominated | Japan government and agencies
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		2,196
Total Unrealized Losses		45
Less than 12 months Fair Value		2,196
Less than 12 months Unrealized Losses		45
12 months or longer Fair Value		0
12 months or longer Unrealized Losses		0
Yen-denominated | Mortgage- and asset-backed securities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		36
Total Unrealized Losses		1
Less than 12 months Fair Value		36
Less than 12 months Unrealized Losses		1
12 months or longer Fair Value		0
12 months or longer Unrealized Losses		0
Dollar-denominated | Public utilities
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		301
Total Unrealized Losses		15
Less than 12 months Fair Value		181
Less than 12 months Unrealized Losses		8
12 months or longer Fair Value		120
12 months or longer Unrealized Losses		7
Total Fair Value	306
Total Unrealized Losses	10
Less than 12 months Fair Value	69
Less than 12 months Unrealized Losses	2
12 months or longer Fair Value	237
12 months or longer Unrealized Losses	8
Dollar-denominated | Sovereign and supranational
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		35
Total Unrealized Losses		7
Less than 12 months Fair Value		35
Less than 12 months Unrealized Losses		7
12 months or longer Fair Value		0
12 months or longer Unrealized Losses		0
Dollar-denominated | Banks/financial institutions
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		60
Total Unrealized Losses		6
Less than 12 months Fair Value		23
Less than 12 months Unrealized Losses		1
12 months or longer Fair Value		37
12 months or longer Unrealized Losses		5
Total Fair Value	79
Total Unrealized Losses	4
Less than 12 months Fair Value	18
Less than 12 months Unrealized Losses	0
12 months or longer Fair Value	61
12 months or longer Unrealized Losses	4
Dollar-denominated | Other corporate
Investments, Unrealized Loss Position [Line Items]
Total Fair Value		3,625
Total Unrealized Losses		297
Less than 12 months Fair Value		1,329
Less than 12 months Unrealized Losses		70
12 months or longer Fair Value		2,296
12 months or longer Unrealized Losses		$ 227
Total Fair Value	4,261
Total Unrealized Losses	248
Less than 12 months Fair Value	792
Less than 12 months Unrealized Losses	53
12 months or longer Fair Value	3,469
12 months or longer Unrealized Losses	$ 195